The search for a method to efficiently and practically drive a solid state lighting device has been going on for years. Solid state lighting units operate in a fundamentally different way than incandescent or even fluorescent lamps, and generally are not connectable directly to an alternating current (AC) power line. Rather, ballasts or other driving circuits are used to make existing lighting fixtures operable with solid state lighting units.
Ballast circuitry is often complex and expensive, making solid state lighting fixture expensive to operate. Another drawback of most current solid state lighting device ballast circuits is that their controlling algorithms are based on either regulating the output voltage as a “constant voltage” supply or regulating the output current as a “constant current” supply. The regulated voltage and regulated current approaches often are not capable of working with an AC phase control dimmer.
A typical AC phase control dimmer controls the illumination of a lighting fixture by cutting off a portion of the input AC voltage. This results in a decrease in the rectified input direct current (DC) voltage. A voltage or current regulating ballast will sense the decrease in the input DC voltage by increasing the output voltage or current. This counteracts the dimmer's attempt to lower the illumination of the lighting fixture, thereby rendering the dimmer function inoperable or impractical.